Urbanization-driven increases in summertime compound heat extremes across China

Area of Science:

• Environmental Science
• Climate Science
• Urban Climatology

Background:

• Summertime extreme heat events significantly impact human societies and natural environments, especially in urbanized regions.
• Previous research often focused on independent daytime or nighttime heat, neglecting compound heat events occurring on the same day.
• Compound heat events, combining extreme daytime and nighttime temperatures, represent a critical but understudied aspect of heat extremes.

Purpose of the Study:

• To investigate the spatio-temporal changes of summertime compound heat extremes across China.
• To analyze the specific impacts on 20 major urban agglomerations (UAs).
• To quantify the influence of urbanization on these compound heat events.

Main Methods:

• Spatio-temporal analysis of compound heat extremes (compound heat day and compound heatwave).
• Focus on 20 major urban agglomerations (UAs) in China.
• Quantification of urbanization effects on heat event trends.

Main Results:

• Compound heat events exhibit significant spatial disparities across China, being more frequent in highly populated and urbanized areas like the Pearl River Delta.
• The frequency and fraction of compound heat events have notably increased in most of China over recent decades, with accelerated trends in more developed UAs.
• Most UAs show an intensifying urbanization effect on compound heat events, while a few in northwestern and central China exhibit a weakening effect.

Conclusions:

• Urbanization plays a crucial role in amplifying compound heat extremes.
• The increasing threat of compound heat events in urban areas warrants greater attention amidst global warming and ongoing urbanization.
• Targeted adaptation strategies are needed for vulnerable urban agglomerations to mitigate the escalating risks of extreme heat.